1. Field of the Invention
The present invention relates to a transparent conductive layer and an image display device employing the same, and more particularly, to a transparent conductive layer which reduces reflection, shields electromagnetic waves, protects against physical damage, and which is moisture proof and water repellent, and an image display device employing the transparent conductive layer.
2. Description of the Related Art
Transparent conductive layers refer to thin conductive films coated on high-transmittance insulation surfaces. Transparent conductive layers are widely used as anti-static layers and electromagnetic wave shielding layers for home appliances or as transparent electrodes for power supply in flat liquid crystal displays or electroluminescent devices. In recent years an increasing concern about the harmfulness of electromagnetic waves to the human body, which come out of the monitor of image display devices including cathode ray tubes, has increased the need for a multi-functional transparent conductive film having both anti-reflective and anti-static functions.
To shield the electromagnetic waves emitted from the monitor of a display device such as a cathode ray tube (CRT), a conductive layer is formed on a panel surface of the display device. A conductive layer for both electromagnetic wave shielding and anti-static functions should have a low surface resistance of 102-104 Σ/˜.
When a coating composition containing a conductive oxide, such as antimony (Sb)-doped tin oxide or tin (Sn)-doped indium oxide, is used to form a low surface resistance conductive layer, the conductive layer should be thicker than a conventional coated layer to obtain a desired anti-static effect. Therefore, it was unpractical to form a thin electromagnetic wave shielding and anti-static coated layer using a conductive oxide such as Sb-doped tin oxide or Sn-doped indium oxide.
Another approach to form a low surface resistance conductive layer involves use of a conductive layer coating composition containing minute metal particles such as silver (Ag) to form a thin conductive layer. Also, the conductive layer coating composition includes an organic stabilizer, such as polyvinyl alcohol, polyvinyl pyrrolidone, and gelatin, to improve the dispersion of the metal particles in the coating composition.
However, the thin conductive layer formed of the coating composition containing the metal particles has a high grain boundary resistance due to interaction between the particles stabilized by the organic stabilizer, so the surface resistance of the thin conductive layer cannot be lowered. Therefore, there is a need to destroy and remove the organic stabilizer by heating the conductive layer at a high temperature of about 400° C. after being coated.
However, the high-temperature heating performed to destroy and remove the organic stabilizer causes the metal particles to dissolve and aggregate and thereby reduces the transparency of the resulting thin conductive layer. In a transparent conductive layer containing metal particles, especially silver, the metal particles are grown by ionization and the metal is susceptible to oxidize and corrode, thereby lowering the reliability of a display device in terms of thin film conductivity and light transmittance.
To address these problems, Korean Laid-open Patent Publication No. 98-25037 suggested a transparent conductive layer, which comprises a transparent conductive particle layer formed on a substrate and containing composite metal particles, for example, of at least two metals selected from Au, Ag, Rd, Pt, Rh, Ru, Cu, Fe, Ni, Co, Sn, Ti, In, Al, Ta, and Sb, having an average particle size of 1-200 nm, and a transparent coated layer formed on the transparent conductive particle layer with a smaller refractive index than the transparent conductive particle layer.
However, such a transparent conductive particle layer causes many practical problems because the metal particles in the transparent conductive particle layer are oxidized by water vapor and oxygen present in the air. Also, the use of the costly metal particles increases the cost of manufacturing the transparent conductive layer.
A method of forming a transparent conductive layer on the surface of a cathode ray tube as an image display device involves forming a conductive layer by coating a glass panel with a conductive composition, which includes a conductive metal and a solvent, forming a protective layer by coating a silicon alkoxide-containing composition on the conductive layer, and forming a spray-coated layer on the protective layer. However, the transparent conductive layer formed using this method absorbs external moisture and thereby causes spots or stains on the surface. These surface spots or stains often occur during the manufacture and use as well as long-term transportation and storage and are hardly removed, thereby lowering product quality. In addition, the absorption of moisture markedly weakens the intensity of the transparent conductive layer, so that it is easily delaminated and separated.
To solve these problems, the present invention suggests use of a water repellent in the formation of the spray-coated layer to form a conductive layer whose surface is water repellent and wet-endurable with the effect of reducing reflectivity and uses fluoroalkylsilane having a small surface tension as the water repellent (Korean Laid-open Patent Publication No. 2000-50673). Although the water-repellent spray-coated layer shows excellent film hardness and water repellency, the moisture resistance is easily decreased and variations in resistance increase as the composition and thickness of the conductive layer change.